The present invention relates in general to a method and system for operating a camless internal combustion engine. More particularly, the invention relates to a method and system for reducing noise vibration and harshness (NVH) resulting from the operation of intake and exhaust valves in a camless internal combustion engine.
Camless internal combustion engines are well known in the art and are used primarily to provide variability in valve timing, duration and lift. Because valve operation is not dependent on fixed valve timing, duration and lift, such engines can be optimized by varying any or all of these parameters to achieve optimal engine performance. Valves in conventional camless engines are typically actuated using electromechanical or electrohydraulic actuators. Electromechanical actuators use solenoids to generate a magnetic field to attract an armature which in turn actuates one or more corresponding valves and electrohydraulic actuators utilize fluid pressure, controlled by solenoids, to operate one or more corresponding valves. The opening and closing of the valves is typically a function of one or more engine parameters such as speed, demanded engine torque or crankshaft angular position.
Conventional camless engines having electromechanically or electrohydraulically actuated valves, such as described in U.S. Pat. No. 4,794,890 to Richeson and U.S. Pat. No. 5,419,301 to Schechter, however are often susceptible to undesirable noise vibration and harshness (NVH) caused by the contacting or xe2x80x9cslammingxe2x80x9d of actuator components against each other and the contacting of valve components against corresponding valve seats. This condition occurs because the high valve opening velocities required for gas exchange often result in excessive, non-zero xe2x80x9cseatingxe2x80x9d velocities as the valve components contact each other or corresponding valve seats. To complicate matters, accurate velocity control of valve components is often very difficult due to system susceptibilities caused by operating conditions, component degradation and variability of control schemes and devices used to operate the valves.
Known methods for monitoring and controlling seating velocity involve using expensive sensors such as laser interferometers. Such sensors are used to directly measure seating velocity and derive current versus velocity and voltage versus velocity profiles for corresponding electromechanical actuators used to open and close the valves. The current and/or voltage profiles are in turn used to derive appropriate control signals for decreasing the seating velocity. Such techniques, however, are costly and often susceptible to high noise levels and inaccuracies in generated control signals.
Accordingly, the need exists for implementing a more accurate, less expensive method for monitoring and controlling the speed of actuated valves in an internal combustion engine. Such a method is critical for reducing NVH associated with the operation of the camless internal combustion engine.
The aforedescribed limitations and inadequacies of conventional valve control methods for camless internal combustion engines are substantially overcome by the present invention, in which a primary object is to provide a method and system for controlling valve actuation in a camless internal combustion engine while reducing noise vibration and harshness (NVH).
The above object is achieved by a method for operating one or more valves of a camless internal combustion via electronically controlled valve actuators. The method includes the steps of: measuring noise occurring during valve operation; deriving a control signal based at least in part on the measured noise; and applying the control signal to one or more of the valve actuators to reduce noise attributable to valve operation. The method can be applied to individual intake and exhaust valves of a camless internal combustion engine so as to effect a significant reduction in NVH.
Another preferred method is also provided for operating one or more valves of a camless internal combustion engine, the method including the steps of: determining the occurrence of a valve event; defining a vibration measurement window beginning at a predetermined time prior to the valve event and ending at a predetermined time after the valve event; measuring the vibration of the internal combustion engine attributable to at least one of the valves during the vibration measurement window to generate a vibration measurement signal; deriving an energy content signal from the vibration measurement signal; generating a control signal based at least in part on the energy content signal; and applying the control signal to one or more valve actuators coupled to the valves so as to reduce NVH attributable to the operation of the valves. The method further includes the steps of adjusting the magnitude and duration of the control signal based upon whether or not energy content signal is greater than a predetermined maximum amount or less than a predetermined maximum amount.
An advantage of the above methods is that NVH resulting from the actuation and seating of intake and exhaust valves of a camless internal combustion engine is reduced based on direct measurements of the NVH. Through appropriate processing and analysis of the measured NVH, a corresponding control signal is derived and applied to the valve actuators to generate minimal NVH while ensuring proper opening and closing of the valves. This leads to quieter operation of the engine and diminished wear on valve components.
In accordance with another aspect of the present invention, a valve control system is provided for operating one or more of a camless internal combustion engine. The valve control system includes: at least one valve actuator coupled to the valves; at least one sensor for measuring NVH related to the operation of the valves; and an engine controller coupled to the at least one valve actuator and the at least one sensor for controlling the operation of the internal combustion engine and the valves. The engine controller further determines the time of occurrence of NVH-generating valve events associated with the operation of the valves, processes signals representing the NVH measured by the at least one sensor, and generates a control signal for the at least one valve actuator to reduce the effects of NVH attributable to the operation of the valves, the control signal being based at least in part on the measured NVH.
Still further, in accordance with yet another aspect of the present invention, an article of manufacture is provided for operating of one or more valves of a camless internal combustion engine. The article of manufacture including: a computer usable medium; and a computer readable program code embodied in the computer usable medium for directing the computer to perform the steps of: determining the time of occurrence of NVH-generating valve events associated with the operation of the valves; processing signals representing the NVH measured by the at least one sensor; and generating a control signal for one or more of valve actuators coupled to the valves to reduce the effects of NVH attributable to the operation of the valves, the control signal being based at least in part on the measured NVH.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.